1. Field of the Invention
The present invention relates to an external connection terminal and a semiconductor device and, more particularly, to an external connection terminal used in the semiconductor device, the electronic parts, the wiring substrate, the package, etc. and a semiconductor device having projection-like connection terminals.
2. Description of the Prior Art
Solder is employed to connect electrically and mechanically the semiconductor device to the ceramic substrate or to connect electrically and mechanically the electronic parts to the wiring substrate.
For example, the solder is formed on the metal wiring like a ball, or is coated on the metal wiring by screen printing, and then is jointed to the metal wiring by heating/melting. Normally the metal wiring is formed of metal containing a large amount of aluminum (Al) or copper (Cu).
When the solder is jointed to the surface of the metal wiring, normally the nickel (Ni) layer is formed as the diffusion barrier metal (barrier metal) layer between the solder and the metal wiring, for the purpose of preventing the mutual diffusion the constituent element of the metal wiring and the tin (Sn) in the solder. As a method of forming the nickel layer, the employment of the electroless plating method without the feeding terminal is advantageous to shorten the film forming steps and to suppress cost. Also, in order to improve the wettability of the solder, sometimes the gold layer is formed on the nickel layer.
The state before the solder is jointed to the metal wiring on which the nickel layer and the gold layer are formed is shown in FIG. 1, for example. In FIG. 1, the nickel (Ni) layer 103 and the gold (Au) layer 104 are formed on a part of the surface of the metal wiring 102 on the insulating film 101 by the electroless plating method, and the tin alloy solder 105 is placed thereon.
Also, Patent Application Publication (KOKAI) 2000-133739 discloses forming another solder layer made of the material, that has a melting point higher than the tin alloy solder and contains an amount of tin less than the tin alloy solder, on the gold layer 104 by the electroless plating method, etc., before the formation of the tin alloy solder 105.
As another structure of the solder layer and the metal wiring, Patent Application Publication (KOKAI) 2000-22027 discloses forming the nickel plating layer, the palladium plating layer, and the gold plating layer in order on the wiring.
Also, sometimes the gold film is employed in place of the tin alloy solder layer. As the barrier metal film between the gold film and the wiring, it is set forth in Patent Application Publication (KOKAI) Hei 3-209725, for example, to form the nickel film by the electroless plating method.
In addition, as the layer structure of the wiring and the solder layer, various structures have been known.
For example, Patent Application Publication (KOKAD) Hei 9-8438 discloses forming the electroless nickel plating film, the substitutional palladium film, the electroless palladium plating film, the substitutional gold plating film, and the electroless gold plating film in sequence on the surface of the wire bonding terminal.
In Patent Application Publication (KOKAl) Hei 5-299534, the structure in which the first layer made of the electroless nickel plating film, the second layer made of the electroless nickel-boron plating film or the electroless nickel-phosphorus plating film, and the third layer made of the palladium film or the palladium alloy film are formed in sequence on the metal outer ring is set forth as the stem to be soldered. Here the palladium film or the palladium alloy film is formed to improve the wettability of the solder.
Meanwhile, the conductive pins used as the external connection terminals of the semiconductor device are set forth in Patent Application Publication (KOHYO) Hei 9-505439, for example. The surface of the semiconductor device on the conductive pin forming side is covered with the plastic package. Also, the projection electrodes used as the external connection terminals of the semiconductor device are set forth in Patent Application Publication (KOKAI) Hei 5-55278, for example. A real chip size of the semiconductor device on which the conductive pins and the projection electrodes are formed can be achieved.
As described above, the nickel film or the nickel alloy film is formed on the surface of the wiring, the pin, or the stem to which the solder is jointed, and then the layer having a single layer structure or the multi-layered structure made of gold, palladium, or the like is formed thereon.
However, according to such structure, after the solder is jointed to the wiring, the pin, or the stem by the heating/melting, such solder is easily peeled off from the wiring, the pin, or the stem by the external impact, etc.
Patent Application Publication (KOKAI) 2000-133739 discloses that, as the cause of such peeling-off, the concentration of the phosphorus contained in the nickel layer, that is formed by the electroless plating, is increased at the time of melting the solder.
By the way, in the external connection terminals formed on the package of the semiconductor device or on the semiconductor device, there are following respects to be improved.
For example, Patent Application Publication (KOKAI) Hei 5-55278 and Patent Application Publication (KOHYO) Hei 9-505439 both disclose, in the semiconductor device which is miniaturized to the same size as the chip, the capability of relaxing the thermal stress is lowered rather than the package in the prior art and thus the stress tends to concentrate to the external connection terminal packaging portion.
In the semiconductor device set forth in Patent Application Publication (KOKAI) Hei 5-55278, the plastic sealing is formed only on one surface of the silicon chip, and side surfaces and the back surface of the silicon chip are exposed. Because silicon is very fragile, there is a possibility that, if the silicon chip is thinned more and more, the circuits formed in the chip are damaged by the silicon chipped off from the exposed surface side.
That is, in the package which is miniaturized to the same size as the chip, there is a possibility that the chipping or the crack on the back surface or the side surfaces causes the damage of the circuits and thus yield of the fabrication is lowered.
Patent Application Publication (KOHYO) Hei 9-505439 aims at improvement of the packaging reliability by forming the electrode on the metal pad by using the deformable metal wire. This electrode can be formed by the normal wire bonder method, but the formation tact needs the time that is several times the normal bonding and also needs much production cost. Also, the electrode made of the metal wiring is covered with the metal shell formed by the electrolytic plating method. In this case, if the electrolytic plating is applied in the situation that the wiring patterns connected to the metal wiring are exposed, the distribution of the film thickness of the metal shell is largely affected by the distribution of the current density in the electrolytic plating. Thus, because it is difficult to obtain sufficient and uniform thickness, it is difficult to achieve the fine pitch of the electrode made of the metal wire. In addition, if the metal shell is formed by an electrolytic plating method and then the wirings are formed by etching the metal film, migration of the wiring material becomes a concern.
Also, Patent Application Publication (KOHYO) Hei 9-505439 discloses that pin-like metal wires are covered with a nickel layer and a gold layer and then the metal wires are connected to the external devices by solder. In this case, if the nickel layer is formed by the electroless plating method, there is a possibility that crack is created between the solder and the metal wire, as described above.
It is an object of the present invention to provide an external connection terminal having a new joint layer structure that can improve the adhesiveness between the metal pattern used as the electrode, the wiring, or the pad and the solder.
Also, it is another object of the present invention to provide a semiconductor device that can achieve the improvement of yield.
According to the present invention, the external connection terminals are constructed by forming the phosphorus-containing or boron-containing nickel layer, the rich phosphorus-containing or rich boron-containing nickel layer that contains the phosphorus or the boron higher than this phosphorus-containing or boron-containing nickel layer, the nickel-tin ally layer, the tin-rich tin alloy layer, and the tin alloy solder layer in sequence on the electrode.
Also, according to the present invention, the external connection terminals are constructed by forming the phosphorus-containing or boron-containing nickel-copper layer, the rich phosphorus-containing or rich boron-containing nickel-copper layer that contains the phosphorus or the boron higher than this phosphorus-containing or boron-containing nickel-copper layer, the nickel-copper-tin ally layer, and the tin alloy solder layer in sequence on the electrode.
According to such external connection terminals, after the tin alloy solder layer is heated/melted to exceed the melting point, a Kirkendall void to weaken the external connection terminal is not generated. Therefore, the adhesiveness between respective layers can be improved and thus the reliability of the external connection terminals can be enhanced.
Also, according to the present invention, in the chip-like semiconductor device having the projection-like electrodes, the coating film made of organic insulating material or metal is formed on at least one of the back surface and the side surfaces of the semiconductor substrate. Therefore, it is difficult for chipping or cracking to occur on the back surface and the sides surfaces of the semiconductor substrate, and, thus, the yield of the semiconductor devices can be improved by preventing the damage of the semiconductor circuits.
In addition, because the metal patterns to which the external connection terminals are connected are covered with the organic insulating film having the low hygroscopic degree, generation of the migration of the metal patterns can be prevented and thus the reliability of the package can be improved. Also, because any one of copper, aluminum, and gold is employed as the electrodes and the wirings, the semiconductor devices in which the electrodes and the wirings are excellent in electric conduction and heat radiation can be formed at low cost by the existing equipment.
Further, because the external connection terminals are formed like a rod such as the circular cylinder, the polygonal column, etc., the length can be enlarged not to extend the interval between the external connection terminals, and, thus, a fine pitch of the external connection terminals can be achieved.
Besides, because the external connection terminals are formed in a straight line, the external connection terminals can be formed at the short tact by the existing equipment in executing the wire bonding.
With the above, the possibility of the migration of the wiring material is wiped away and also the fine pitch between the projection-like electrodes is achieved.